The invention relates to a process for the manufacture of a metallic composite wire having a core made of a hard material and a sheath made of a relatively soft material wherein a rod made of the core material is inserted into a pipe made of the sheath material. The cross section of this arrangement is reduced to a prescribed value by means of drawing.
A process of this kind is known from U.S. Pat. No. 3,848,319. It is employed for the manufacture of very thin wires made of a noble metal or a noble metal alloy. After the drawing, however, the sheath-material is chemically removed by etching. The core material is pure gold, and the sheath material is copper. In order to avoid diffusion between the gold and the copper or vice-versa, this known process does not employ heating steps.
U.S. Pat. No. 4,291,644 also discloses a process for the manufacture of a composite wire where a hard core material is provided with a soft sheath material by means of extrusion. The core is heated up by passing a current directly through it while it is kept under constant tensile stress, which can amount to 50% of the tensile strength of the core material. The core material is steel, for example, and the sheath material is aluminum.